Method of making pressure containers



DeC. 26, 1944. s w ALDERFER 2366,14]

METHOD OF MAKING PRESSURE CONTAINERS Filed June 25, 1943 Svzmme w. ALDEQFER Patented Dec. 26, 1944 UNITED STATES n'm'rnon or MAKING ranssuaa commas Sterling w. Alder-fer, Akron, Ohio, asslgnor a one-half to Edward D. Andrews, Akron, Ohio Application June 25, 1943, Serial No. 492,323

1 Claim. (Cl. air-dear) The present invention relates to the manufacture of containers designed to hold fluids or gases under high pressures in which the container is composed in whole or in part of a length of metallic tubing in coiled form. The advantages of containers of this type are fully set forth in my copending applications Serial No. 452,979, filed July 30, 1942, and Serial No. 462,628, filed October 19, 1942, the former being directed to a container comprising a coil of pipe with the valves and fittings by which it is adapted to be attached to an inflatable article such,for example, as a life raft. The latter relates to a novel type of container in which there is located a central core or cylinder about which is wrapped a coil of the piping communicatingwith the interior. of the cylinder and constituting a secondary chamber for the pressure medium.

The problem in connection with the manufac ture of containers of the types described is in the maintenance of a fixed volume for the coil of tubing. When flexible metal tubing is wrapped either about a central, permanent core or about a forming mandrel, the tension exerted by the winding operation will cause the tubing to collapse, making it impossible to hold a given internal volume. The collapsing of the tube also weakens the tube and causes fractures to start in the tube or premature failure. It is essential that the containers be able to withstandvery high pressures indefinitely and the elimination of failures due or traceable to distortion of the tubing during winding is a very substantial improvement in the art.

By the method which has been shown and described herein, the various problems have been met and it is possible easily and rapidly to construct containers of the types specified which will meet the most rigid requirement both as to the volumetric capacity of thecompleted container and the ability to withstand high internal pressures.

In the drawing and description the best known and preferred method of making two types of containers is shown, it being understood that the principles of the invention may be applied to the manufacture of other containers which embody a length of pipe, preferably in coiled form, v

the coil of tubing is wound to constitute a secondary or auxiliary chamber and to serve as a reinforcement for the walls of the core. Fig. 1

shows the arrangement of the parts in the first step of the operation; Fig. 2 shows the core par- ,tially wound; and Fig. 3 is a section through a Primarily they are intended to carry a very concentrated charge of CO2 gas under high pressure and are attached to life belts or life rafts so that upon the opening of a valve the gas will expand and inflate the object. Aiurther extension of their use is in the supplying of oxygen. for high altitude flying or parachute work, the containers being carried by the aviator or attached to the parachute and provided with a breather pipe and necessary valve controls. One advantage of containers of the type illustrated is that a light, relatively soft metal stock may be used for the tubing which will be easy to coil and which will not shatter ii punctured and scatter destructive fragments. One of the objections to a heavy cylinder such as used for the purpose was in the deadly effect of scattered particles. A further advantage is that, due to the limited cross-sectional area of the tube, the destructive force exerted by the pressure is relatively low and, therefore, a cheaper, thin metal wall may be employed for the tubing which not only reduces the expense but makes a safer container.

The difllculty, however, in the manufactureof containersof the type specified from tubing is due to the tendency of the tubing to be collapsed or deformed during the coiling operation. For overcoming this objection, the tubing is filled with water or some equivalent liquid under asufficiently high pressure so that the tube retains its original volume against the stresses exerted in winding the tubing about a coreor mandrel. The tubing will be deformed from its full round shape, being slightly flattened, but as the interior volume of the tube is unchanged due to the pressure of the water, the walls of the tube will stretch sufliciently to retain the original volume. The extent of pressure applied to the water which fills the tube is dependent upon a number of factors which have to be considered in arriving out collapse.

- valve fitting 2 which is closed during the opera tion described. Set within the wall of the core,

carbon content of .05-.15 with an outer diameter of 1's" and a wall thickness of .022" to be wrapped in a coil having a 1"'di ameter (i. e., about a core with 1" outer diameter), from 2500 to 2600 lbs. of hydrostatic pressure is supplied to the tube. It will be'found that pressure of this degree is maintained substantially constant on the gauge 8 against the forces required to wrap the tubing usually by a ferrule connection 3, is the length of metal tubing 4 which is to form the coils about the core, the usual form of container of this type comprising one ormore complete wrapplngs over the length of the core.

Connected to the end of the tubing 4 by the releasable union 6 is a length of rigid pipe 7 provided with a branch leading to a pressure gauge 8. Also connected to the pipe is a valve I0, Beyond the valve is the releasable union l2 to a supply line H which leads from any source of hydrostatic pressure, suchas a pump or accumulator.

In the operation, the elements being assembled as shown, the valve In is' opened and water under the predetermined pressure is admitted to the tubing 4 and the core I. The extent of the pressure will be indicated by the gauge 8. When the pressure is raised to the proper point within the tubing and core, the valve I 0 is closed and the connection I2 is freed.

The core I with the attached tubing is then mounted in an ordinary lathe or rotating holder and rotated'while the operator holds the free end of the pipe and guides the coils of pipe so they lie evenly and regularly about the core. A sufiicient hold-back is exerted upon the tubing to cause it to wrap in snug, close fitting coils about the core and about the underlying coils. During the winding operation the forces exerted on the tube will cause it to flatten somewhat, but as the water or other fluid is substantially incompressible, any reduction in area due t deformation from the round tube will be compensated for by the stretching of the tube walls, and the exact and predetermined capacity of the tub-. ing is maintained. The core I constitutes a mandrel or form about which the coils are wrapped which becomes a permanent part of the container.

The extent of pressure exerted upon the water which fills the assembly is determined by that pressure which insures that there is no collapsing of the tube. This pressure is, roughlyspeaking, equal to the force required to wind the-tube withing the winding of a coil of even diameter, but as the diameter of the coil increases, as in the outer layers of a container such as shown in Fig. 1, or in winding a coil of increasing diameter as in Fig. 4,

the force required to bend the coil will decrease and the pressure will decrease proportionately therewith. By way of example merely, the following are given.

For a steel tubing composed of a relatively soft steel designated as .1010 steel under the recognized SAE standards, which has approximately a It will be appreciated that the pressure within the tubing will remain constant dursnugly about the core during the winding of the first turn of the coil.

- As a second example, a tubing composed of 53 SO aluminum of /2" outer diameter and a wall thickness of .035" wrapped in a coil of 4-inch internal diameter will require from 400 to 500 lbs. internal pressure to prevent collapse.

With the formulae given, it is possible to arrive at the proper pressure with any variation in the several factors, it being essential only that the pressure employed be adequate to retain" the "predetermined volumetric capacity which may be found by observing the behavior of the gauge during the winding operation.

If, in the winding operation, there is a sudden drop in pressure, it is indicative at once that a leak has developed. The method has the. added advantage, therefore, of detecting any fault in the structure.

In the making of the flat or pancake" type of container, a similar procedure is followed, the difference being that instead of a core which provides a mandrel that remains as a permanent part of the container, a temporary mandrel such as indicated at 20 is employed. As shown in the drawing, this is a cone-shaped mandrel, but any form of mandrel may be employed, dependent upon the shape of the finished coil. The end of the tubing 4 is capped as at 2|, the connections at the other end of the tubing being the same. A keeper 22 is provided on the core to hold the 40 leading end of the tubing. The wrapping is started while the requisite pressure is maintained in the tubing by closing the valve I0 after the tub ing is filled. As the diameter of the coil increases, the reading on the pressure gauge will diminish at 'a substantially uniform rate. When the coil is completed, the connection 23 is freed and the coil removed from the mandrel. It may then be flattened out to the "pancake form. In

, the making of a permanently conical or cylindrical coll the mandrel may be altered desired form to the coil.

It will be understood that other fluids besides water may be employed, but water is an ideal medium for the purpose.

What is claimed is:

to give the The method of manufacturing a pressure con- STERLING W. ALDERFER. 

